According to MacStories, Apple will release iOS 4.3 on Valentine's Day, February 14.
It is rumoured that the new version will incorporate Apple's new Personal Hotspot function, allowing mobile WiFi internet sharing. This is perhaps the most significant novelty, but these are still rumours, so take everything with a grain of salt.
In addition iOS 4.3 will sport improved AirPlay support and a few tweaks for the iPad, including support for app subscriptions, introduced with The Daily, Rupert Murdoch's iPad-only magazine. The update will also allow for more, bigger ads in more apps, which is hardly good news.